Simulation-based safety analysis of diversion and confluence area in urban underground loop

The underground loop interconnected with the underground space of the urban CBD area has multiple entrances and exits, forming multiple traffic diversion or confluence areas, which greatly affects the traffic operation safety of the underground loop. In this study, the traffic conflict technique is used to investigate safety of the traffic diversion and confluence area of the urban underground loop with the consideration of the traffic conflicts, speed difference, Time to Collision (TTC), and Post Encroachment Time (PET) as evaluation indexes. VISSIM is used to simulate the vehicle trajectory which is then analyzed using SSAM to identify the traffic conflict condition in the traffic diversion and confluence area in the loop. Based on this, the traffic conflict safety evaluation model is established using the traffic conflict rate and conflict severity, and safety assessment is carried out taking an underground loop as an example. The results show that the simulation method can better evaluate the traffic conflict risk in the diversion and confluence area of the underground loop and can be used for the safety analysis of the proposed and new underground loop.